Class IntSumOfSquares

  • All Implemented Interfaces:
    java.util.function.DoubleSupplier, java.util.function.IntConsumer, java.util.function.IntSupplier, java.util.function.LongSupplier, IntStatistic, StatisticAccumulator<IntSumOfSquares>, StatisticResult

    public final class IntSumOfSquares
    extends java.lang.Object
    implements IntStatistic, StatisticAccumulator<IntSumOfSquares>
    Returns the sum of the squares of the available values. Uses the following definition:

    \[ \sum_{i=1}^n x_i^2 \]

    where \( n \) is the number of samples.

    • The result is zero if no values are observed.

    The implementation uses an exact integer sum to compute the sum of squared values. The exact sum is returned using getAsBigInteger(). Methods that return int or long primitives will raise an exception if the result overflows.

    Note that the implementation does not use BigInteger arithmetic; for performance the sum is computed using primitives to create an unsigned 128-bit integer. Support is provided for at least 263 observations.

    This class is designed to work with (though does not require) streams.

    This implementation is not thread safe. If multiple threads access an instance of this class concurrently, and at least one of the threads invokes the accept or combine method, it must be synchronized externally.

    However, it is safe to use accept and combine as accumulator and combiner functions of Collector on a parallel stream, because the parallel implementation of Stream.collect() provides the necessary partitioning, isolation, and merging of results for safe and efficient parallel execution.

    Since:
    1.1
    • Field Summary

      Fields 
      Modifier and Type Field Description
      private static int SMALL_SAMPLE
      Small array sample size.
      private UInt128 sumSq
      Sum of the squared values.
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void accept​(int value)
      Updates the state of the statistic to reflect the addition of value.
      IntSumOfSquares combine​(IntSumOfSquares other)
      Combines the state of the other statistic into this one.
      static IntSumOfSquares create()
      Creates an instance.
      java.math.BigInteger getAsBigInteger()
      Gets the sum of squares of all input values.
      double getAsDouble()
      Gets the sum of squares of all input values.
      int getAsInt()
      Gets the sum of squares of all input values.
      long getAsLong()
      Gets the sum of squares of all input values.
      (package private) UInt128 getSumOfSquares()
      Gets the sum of squares.
      static IntSumOfSquares of​(int... values)
      Returns an instance populated using the input values.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
      • Methods inherited from interface java.util.function.IntConsumer

        andThen
    • Field Detail

      • SMALL_SAMPLE

        private static final int SMALL_SAMPLE
        Small array sample size. Used to avoid computing with UInt96 then converting to UInt128.
        See Also:
        Constant Field Values
      • sumSq

        private final UInt128 sumSq
        Sum of the squared values.
    • Constructor Detail

      • IntSumOfSquares

        private IntSumOfSquares()
        Create an instance.
      • IntSumOfSquares

        private IntSumOfSquares​(UInt128 sumSq)
        Create an instance.
        Parameters:
        sumSq - Sum of the squared values.
    • Method Detail

      • create

        public static IntSumOfSquares create()
        Creates an instance.

        The initial result is zero.

        Returns:
        IntSumOfSquares instance.
      • of

        public static IntSumOfSquares of​(int... values)
        Returns an instance populated using the input values.
        Parameters:
        values - Values.
        Returns:
        IntSumOfSquares instance.
      • getSumOfSquares

        UInt128 getSumOfSquares()
        Gets the sum of squares.

        This is package private for use in IntStatistics.

        Returns:
        the sum of squares
      • accept

        public void accept​(int value)
        Updates the state of the statistic to reflect the addition of value.
        Specified by:
        accept in interface java.util.function.IntConsumer
        Parameters:
        value - Value.
      • getAsInt

        public int getAsInt()
        Gets the sum of squares of all input values.

        When no values have been added, the result is zero.

        Warning: This will raise an ArithmeticException if the result is not within the range [0, 2^31).

        Specified by:
        getAsInt in interface java.util.function.IntSupplier
        Specified by:
        getAsInt in interface StatisticResult
        Returns:
        sum of all values.
        Throws:
        java.lang.ArithmeticException - if the result overflows an int
        See Also:
        getAsBigInteger()
      • getAsLong

        public long getAsLong()
        Gets the sum of squares of all input values.

        When no values have been added, the result is zero.

        Warning: This will raise an ArithmeticException if the result is not within the range [0, 2^63).

        Specified by:
        getAsLong in interface java.util.function.LongSupplier
        Specified by:
        getAsLong in interface StatisticResult
        Returns:
        sum of all values.
        Throws:
        java.lang.ArithmeticException - if the result overflows a long
        See Also:
        getAsBigInteger()
      • getAsDouble

        public double getAsDouble()
        Gets the sum of squares of all input values.

        When no values have been added, the result is zero.

        Note that this conversion can lose information about the precision of the BigInteger value.

        Specified by:
        getAsDouble in interface java.util.function.DoubleSupplier
        Returns:
        sum of squares of all values.
        See Also:
        getAsBigInteger()
      • getAsBigInteger

        public java.math.BigInteger getAsBigInteger()
        Gets the sum of squares of all input values.

        When no values have been added, the result is zero.

        Specified by:
        getAsBigInteger in interface StatisticResult
        Returns:
        sum of squares of all values.